When working fields with self-propelled or towed agricultural equipment such as tractors, swathers and sprayers it is important not to overlap and rework areas of the field, or to leave gaps between worked areas leaving portions of the field idle. Both overlapping and leaving gaps can lead to a decrease in field efficiency which can be wasteful and expensive.
In an attempt to prevent this problem from occurring various navigational aids have been developed in the past to try to help the driver of the vehicle to align the vehicle a distance from the last pass by the vehicle so that the self propelled or towed equipment will not overlap or miss areas. These navigational aids have included such things as foam and disk markers for marking the field, tram lines, and global positioning systems.
As well as these methods various means for sighting along a marked line or along an edge of the worked portion of the ground have been developed. These sighting methods are often mounted externally of the vehicle making adjustment difficult, or involve complex mechanisms for calibrating and adjusting lines of sight. Many of these sighting devices are fixed making them difficult to adjust to suit different drivers or to suit the use of different types of equipment. Furthermore these sighting devices are often difficult to realign after turning and can be difficult to install often requiring modifications to the vehicle or special hardware.